In recent years, technologies for fluorescently labeling biological cells and the like have been attracting attention, and technologies involving the use of the nanoparticles of cadmium selenide (CdSe) and zinc oxide (ZnO) as light emission sources have started to be developed. Both of CdSe and zinc oxide are suitable as light emission sources because: CdSe can serve as a quantum dot to develop a desired color and has a sharp spectrum; and zinc oxide is a material free of toxicity on living organisms.